At present, finishing of leathers is generally performed semiautomatically in tanning-tawing apparatus, with whole hides. This finishing is performed in several stages, including spraying onto the hides by means of a spray gun the finishing products in solution or dispersion in a solvent or aqueous medium and in drying the hides, generally in air convection tunnels heated to 70-80.degree. C., these stages being repeated until a satisfactory finishing layer is obtained.
Such a finishing technique requires drying for a very long period, so as to evaporate totally the solvents or water used which constitute 80 to 95% of the finishing product, as well as very large drying installations.
Further, the drying causes a certain pollution, especially by evaporation of the solvents, and requires a great deal of storage capacity, since about 8 days are necessary to perform the finishing of a single hide.
Further, patent application GG-2 031 000 is known which describes a leather-coating product. This product is a compound photopolymerizable under UV consisting of 40 to 90% by weight of a prepolymer of acrylates and methacrylates and styrene and 10 to 60% by weight of urethane-acrylates. It does not comprise 100% of active materials but also contains nitrocellulose and is diluted in organic solvents so as to be able to be applied in batch by vaporization. Although crosslinking is performed under UV, it is necessary to wait for the total evaporation of the solvent which requires much time and involves a considerable consumption of this expensive and dangerous product. Further, it is not possible to treat the leather continuously, and the coating product can be applied only once, which considerably harms its quality.
Said finishing techniques also involve numerous handlings by repeated taking up of the hides for drying and application of the product and they therefore are generally performed in the tannery only with whole hides or ones cut into strips.
Finally, the relatively large apparatus necessary for the finishing operations require the treatment of a large number of hides to be profitable.
Now the present trend of markets located downstream from the tannery-tawery, particularly in the garment and shoe industry, is toward increasing diversity of series, corresponding to a growing demand by the clientele for new lines or stocks. This great diversity of series imposes changes in color, of finishing products, which are difficult to perform quickly because of the unwieldiness of existing installations.